1. Field of the Invention
The present invention relates to a printer for printing on a recording medium and to a method of controlling the printer (without imposing any restriction regarding the material of the recording medium it will hereinafter be referred to simply as xe2x80x9cpaper sheetxe2x80x9d).
2. Description of the Related Art
There is a kind of printing apparatus that is capable of printing predetermined characters on a paper sheet, such as a corporate or personal check, and is also capable of reading MICR (Magnetic Ink Character Recognition) characters recorded on the paper sheet. Conventionally, with such kind of apparatuses, the paper sheet is transported through a certain paper path and back-side printing (printing on the side of the paper sheet opposite to the side carrying MICR characters) is performed at an upstream side of the paper path, while front-side printing, based on the information read from the MICR characters, is performed thereon at a downstream side of the paper path.
For such back-side printing and front-side printing, dot impact type printing mechanisms are used that employ an ink ribbon supplied from an ink ribbon cartridge. A certain length of ink ribbon is exposed outside of the cartridge and extends between a printing head of the printing mechanism and the paper sheet. To always renew the exposed portion of the ink ribbon, an ink ribbon feeding device is controlled such that fresh ink ribbon is pulled out from one end of the cartridge while about the same length of used ink ribbon is returned at another end into the cartridge.
With such conventional apparatuses, problems result from the fact in that the frequency of back-side printing is far smaller than that of front-side printing, and the ink ribbon feeding devices are driven in accordance with their use. So, the same portion of the ink ribbon used for back-side printing remains exposed for long periods of time and tends to dry up, which results in printing defects.
JP-U-3-95263 describes a printer having an ink ribbon feeding device which is driven for a certain amount of time to feed the ink ribbon by a predetermined amount each time the printer is switched on. While this could solve the problem of dried ink ribbons in some cases, the primary use of the apparatus described above is for POS systems, where the power switch of the apparatus once turned on remains on all day. In such a case, there may be no opportunity for the ink ribbon to be sufficiently fed to the extent that drying of the exposed portion of the ink ribbon can be sufficiently prevented. This is even more true in shops operating on a 24-hour basis.
On the other hand, in case that some or all of the leading edge of the paper sheet is bent or curled, it may be caught by the ink ribbon as it moves past the printing head. If this occurs repeatedly, the ink ribbon may gradually loosen and eventually fall loose from the printing head.
It is an object of the present invention to provide a printer which prevents drying and loosening of an ink ribbon, so as to perform smoothly.
It is another object of the present invention to provide an improved printer suitable for POS systems.
In accordance with the present invention, the ink ribbon is fed by a certain amount each time or each predetermined number of times a paper sheet is detected at a predetermined position within the paper path. The certain amount is sufficient to prevent a degree of drying and loosening of the ink ribbon that could cause printing defects.
The present invention is particularly suitable for a printer comprising two separate printing mechanisms for front-side printing and back-side printing, respectively, as explained above. In this case, regardless of whether back-side printing is performed or not, the ink ribbon for back-side printing is wound up each time a paper sheet is processed in the printer. Thus, drying of the ink ribbon can be prevented even if back-side printing is not performed for long periods of time.
Other objects and attainments together with a fuller understanding of the invention will become apparent and appreciated by referring to the following description and claims taken in conjunction with the accompanying drawings.